Chapter 4: Thermally Driven Heat Pumps for Cooling
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SOLAR COOLING WITH ADSORPTION CHILLERS
Ingo Daßler, Walter Mittelbach, SorTech AG, Zscherbener Landstraße 17
D-06126 Halle, Germany, walter.mittelbach@sortech.de
Abstract: Solar cooling for small-scale application is quite a new topic if it comes to practical
applications. SorTech AG, founded in 2002, is one of the few manufactures of small scale
adsorption chillers and on the market for 5 years now. Within this time over 200 projects
were established all over the world. With these projects a lot of experience in planning,
installation, and operations of thermal cooling systems has been gathered.
As an example a solar cooling installation in Austria will give an insight of performances,
efficiencies, and potentials of this technology.
Keywords: solar cooling, thermal cooling, adsorption chiller, SorTech AG,
SolCoolSys, solar cooling installation
1 OVERVIEW
The following paper shows an example of the strong influence of installation on the
performance of a solar air-conditioning system. The data given are drawn from a project
which was carried out within the German funded project “SolCoolSys”, targeting at the
development of standard solar cooling applications. The installation was performed in
Mürzzuschlag, Austria with the collaboration of the companies SOLVIS and PINK. The
system was monitored by Fraunhofer ISE.
The paper exhibits the performance data after the first installation and again after a
subsequent adaption of the hydraulics and the control strategy, which lead to a significant
increase in cooling capacity and electrical COP. Furthermore, a detailed analysis is given
how installation conditions are affecting the performance data of the adsorption chiller.
2 COMPANY’S PROFILE
SorTech AG, founded in 2002 as a spin-off of the German Fraunhofer-Institut für Solare
Energiesysteme ISE, is one of the first companies in Europe which offers commercial
products for small scale solar cooling application. Since 2007, SorTech offers silica gel
based adsorption chillers with cooling capacities starting from 5 kW to 15 kW per unit (see
Figure 1). In the meantime more than 200 projects mainly in Europe, but as well in Africa,
North America, Asia, and Australia could be realized with cooling capacities up to 150 kW
(e.g. Patent Office in Munich).
In addition to the adsorption chillers SorTech AG product portfolio covers:
standard cooling packages, consisting of chiller, heat dissipation unit, and hydronic
pump station,
customized cooling systems,
detailed planning and installation support.
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3.1 Technical facts
Basic technical facts of the installation are shown in Table 1.
Table 1: Technical facts of installation
A gas burner and two hot water storages have been installed to provide the system with
heat, independently of solar radiation and to bridge operation phases with high thermal
energy consumption (e.g. at the beginning of each sorption cycle).
Figure 4: Hydronic diagram of connections
The system has been equipped with additional components to provide free cooling (using the
heat dissipation unit for cooling at low ambient temperatures) and heating as well. Due to the
lack of practical and performance experiences of solar cooling systems this system has been
monitored. Therefore temperature sensors, flow meters, electric meters, etc. were installed in
order to measure the behavior and the performance of the system. The results were
analyzed and provide the basis for improvements of the system. The results of this
monitoring are given in the next paragraph.
Chiller type
ACS08; 8kW cooling capacity at nominal conditions
Primary Heat (hot temperature)
source
31 m²; flat panel
Secondary Heat source
gas burner
Heat (middle temperature) sink
heat dissipation unit with spraying system (type RC08)
Cooling task (chilled water):
Workshop studio and bureau via fan coil units
Year of commissioning
June, 2011
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3.2 Results
The main focus of the monitoring is set to cooling capacity and electrical COP as
performance and efficiency parameters. The cooling capacity is determined by the three
temperature levels of the adsorption process. The electrical COP, as the ratio of cooling
power and electrical consumption of common auxiliaries, is mainly determined by the heat
dissipation unit with the highest electrical consumption of the system.
The definition of the electrical COP is similar to the definition of the COP of conventional
systems and shows the main advantages of thermal cooling systems: electrical energy is
only used for common auxiliaries (e.g. pumps, heat dissipation units, controlling). The
electrical COP of thermal systems, therefore, can reach a multiple of conventional systems.
Figure 5 shows typical charts of the monitoring (displayed period: approx. 4 hours around
midday):
Figure 5: Chart example: characteristic of the solar cooling system
Upper diagram - electrical consumption of the heat dissipation unit:
To reduce the electrical consumption the heat dissipation unit adapts the speed of its fans to
the cooling load – the lower the load, the lower the speed and electrical consumption. At the
beginning of operation the heat dissipation unit runs at maximum speed to achieve the
cooling task. Along with operation time the speed is reduced to a minimum due to lower
cooling loads.
Lower diagram - heat flows:
Here the typical characteristic of the heat flows (driving heat – red chart, dissipation heat –
green chart, and cooling power – blue chart) are shown with its high peaks at the beginning
of each sorption cycle.
In the following the improvement of the solar cooling system is shown. Therefore, the results
for cooling capacity and electrical COP before and after system improvements are compared
to each other. The results have been achieved under similar weather conditions and
representing average values of a one day monitoring. The monitoring of the system started in
summer 2011. During winter and spring 2012 the improvement of the system took place.
The results after commissioning of the solar cooling system are shown in Table 2.
Table 2: Results before improvements
Cooling capacity
max. 3 kW
Electrical COP
< 5
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The performance and efficiency is below expectation. In order to improve the system’s
performance and efficiency both, constructional and control oriented adaptations have been
done based on the monitoring results. Basic adaptations of the systems are shown in Table 3.
Table 3: Monitored effects and adaptation of the system
After the first monitoring phase the system could be improved due to the adaptations. Actual
performance and efficiency of the system is shown in Table 4.
Table 4: Results after improvement
4 FACING CHALLENGES
These results and the experiences with other solar and thermal cooling systems show,
performance and efficiency depend, like in any other applications, on correct planning,
installation, and operation. Table 5 shows different operation parameters and the effect on
performance and efficiency. To give an idea of the effects the impact of each parameter on
performance and efficiency is given in numbers for a concrete example.
Example:
A cooling task is given with 5.5 kW cooling load and a predicted electrical COP of approx.
11.2.
Table 5: Effects on performance and efficiency
Monitored effect
Effect on the system
Reason & System adaptation
High temperature
differences between heat
dissipation unit and ambient
temperature
High heat dissipation
temperature and therefore low
cooling power and electrical
COP
Heat exchanger was
connected wrongly
reconnecting heat
exchanger
Wrong control strategy of
heat dissipation unit
control algorithm has been
updated
Cooling power to low
Risk of condensation on
cooling devices due to low
temperature
Low electrical COP
Full cooling load was not
yet available
expanding cooling task
Cooling capacity
3 to 5 kW
Electrical COP
6 to 15
Parameters influencing the performance
Effect on performance
Flow rate of driving and cooling circuits are less than nominal
flow rate (e.g. – 200l/h each)
- 10% (5kW instead of 5.5kW)
Insufficient air bleeding of hydronic system
- 5% (5,3kW instead of 5.5 kW)
Driving Heat temperature is less than planned (e.g. 65°C
instead of 75°C)
- 25% (4.1kW instead of 5.5kW)
All effects
- 40% (3.3kW instead of 5.5 kW)
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Our experiences of more than 5 years solar cooling for small scale application in Europe show:
Robust operation mode of the adsorption chiller and good performance are shown in
over 200 SorTech installations
Solar Cooling means today: detailed planning
Concept and dimensioning are crucial factors for the energetic and monetary
outcome: „rules of thumb“ do not work!
Not every application is suited for thermal cooling! (e.g. very low cold water
temperatures are reached only efficiently under certain conditions.
5 SUMMARY AND POTENTIAL
Experiences show that solar cooling can be a good alternative to conventional cooling
systems. The market for thermal cooling, however, is still small but high potential due to
ecological and economical advantages. Besides solar cooling application the market for
thermal cooling using waste heat at low temperature level (<100°C for absorption systems;
<80°C for adsorption systems) and the combination of co-generation units with sorption
chiller is promising. Nevertheless, for market development the following issues are crucial for
the success of thermal cooling in future:
Reducing cost for both, chiller and components
Increasing power-to-mass-ratio
Developing of standard systems for easy installation and operation
Increasing awareness level of solar cooling technology.
6 NOMENCLATURE
ACS08 Adsorption Chiller Silica Gel, 8 kW nominal cooling capacity
Electrical COP ration of cooling power and electrical power of auxiliary equipment
Pth_MT (thermal) dissipation heat
Pth_HT (thermal) driving heat
Pth_LT cooling power
RCS08 heat dissipation unit
7 ACKNOWLEDGEMENTS
We would like to thank:
Projekträger Jülich PtJ for supporting the research within the “SolCoolSys”- Project
Solvis GmbH for installation support
Fraunhofer Gesellschaft ISE, Freiburg for installing the monitoring system and data analysing
Pink GmbH for supervising the installation in Mürzzuschlag, Austria
Parameters influencing the efficiency
Effect on efficiency
wrong pumps (e.g. low end pumps instead of high efficiency
pumps)
- 10% (10.1 instead of 11.2)
higher T in heat dissipation cycle due to wrong installation
(e.g. heat exchanger)
- 38% (7 instead of 11.2)
All effects
-42% (6.5 instead of 11.2)
